WHEN the Skagit River bridge tumbled down last year and snarled traffic on Interstate 5, advocates for a state transportation package said it made a compelling case for a gas-tax increase. Now a report by federal investigators seems to bolster an argument made by critics: The state Department of Transportation (DOT) needs to be smarter.

The immediate cause of the accident has never been in dispute. A truck with an overheight load smacked into low-hanging trusses on the outside lane of the bridge, smashing girders like matchsticks: the truck’s fault. Yet the National Transportation Safety Board (NTSB) finds that state highway officials demonstrated a chilling obliviousness to danger.

There were no low-clearance signs on the bridge. Truckers with too-high loads were supposed to “move over” to the inside lane, which had plenty of clearance, and they were supposed to know this by checking a state website. The trucking company obtained an oversized-load permit online, which requires it to check clearances. But the report says it failed to consider low clearances on the bridge. So the driver never knew.

The legal responsibility seems clear enough for the state to file $17.1 million in claims against the trucking firm and other parties. That is little comfort to the motorists who landed in the drink, the thousands who endured traffic jams during reconstruction, and the family of the state patrolman who was killed while directing traffic.

Nobody at DOT reviewed the permit. The height of the planned load and the route should have triggered alarm bells. The problem was clear: Annual inspections revealed oversized loads struck the bridge in nine of the previous 10 years. One time, the impact ripped a gouge three inches deep.

The bridge collapse is no case of failing infrastructure. Nor is it cause to replace structurally sound but “functionally obsolete” bridges — absurd considering how many there are. The NTSB, quite reasonably, sees this as a national problem and argues for better permitting procedures and consistent warning signs, especially on bridges like this one.

The state DOT is reviewing its practices. Washington might start by passing a bill sponsored last session by state Sen. Michael Baumgartner, R-Spokane, requiring additional bridge-clearance signage and requiring the DOT to review oversized-load permits.

At a time when passage of a transportation package is critical to relieve congestion and remedy a huge maintenance backlog on the state’s highways, and the DOT’s management has been called into question by a stuck tunneling machine, the last thing the agency needs is another black eye.